Reconfigurable solar photovoltaic systems: a review

Download 3,22 Mb.

Pdf ko'rish

bet	1/3
Sana	07.09.2021
Hajmi	3,22 Mb.
	#168000

1 2 3

Bog'liq
1-s2.0-S2405844020323732-main

Review article

Recon

ﬁgurable solar photovoltaic systems: A review

K.A.Himali Lakshika

, M.A.Kalhan Sandaru Boralessa

, Manoja Kaushali Perera

,

Darshana Prasad Wadduwage

, Vasudevan Saravanan

, K.T.Manjula Udayanga Hemapala

Department of Electrical Engineering, University of Moratuwa, Moratuwa 10400, Sri Lanka

Department of Electrical

\& Electronics Engineering, Arunai Engineering College, Tiruvannamalai 606 603, Tamil Nadu, India

A R T I C L E I N F O

Keywords:

Electrical engineering

Energy

Electrical systems reliability

Renewable energy resources

Renewable energy

Micro-grid

Problems related to solar PV

Recon

ﬁgurable architecture

Solar PV

A B S T R A C T

Even though solar power generation has become an emerging trend in the world, its penetration into the utility

grid as a distributed generation source is not a satisfactory measure due to the inherent issues related to solar

photovoltaic systems (SPVSs). In addressing these issues, microgrids have been identi

ﬁed as suitable integrating

platforms for distributed, clean energy resources such as SPV. Different SPV and microgrid architectures are

available for different applications depending on the resource availability and controllability. Recon

ﬁgurability is

a concept that makes a system adaptable to two or more different environments by effectively utilizing the

available resources. The review explains the applications of recon

ﬁgurable approaches on solar PV systems such

as recon

ﬁgurable PV arrays, power conditioning unit (DC/DC converter, DC/AC inverter), microgrid controller

and topology of distribution network with relevant studies. An analysis is also presented considering the unique

features of recon

ﬁgurable systems in comparison to the static systems.

1. Introduction

Nowadays, there is more consideration towards renewable energy

generation in addressing the growing demand for electricity and life-

threatening environmental impacts resulted by greenhouse gas (GHG)

emission. Today, there is an emerging interest in solar and wind power

generations. Therefore, the government and many other organizations

are willing to provide

ﬁnancial support to increase the penetration of

renewable energy generation into the utility grid. As a result of the high

penetration of distributed generation into the distribution network, it

will transform the existing utility grid into a more complex, unstable,

unreliable structure [

]. A reliable and uninterrupted power supply

can be achieved by developing microgrids that integrate distributed

generation and loads which are located within a small geographical area

[

]. SPV has become the most attractive renewable source due to

its high life span together with low maintenance requirements and costs.

Due to its modular nature and lightweight, transportation and installa-

tion are much easier when compared to other technologies [

,

8

Considering these desirable features, a growth in SPV integration to the

utility grid can be expected. Even though solar photovoltaic microgrids

(PV MGs) can reduce the impact on the distribution network, SPVSs may

suffer from issues related to power reliability, quality and conversion

ﬁciency. Therefore, it is a necessity to modify existing solar PV MG

architectures [

]. SPVSs and microgrids consist of power elec-

tronic interfaces (PEI) which make these systems highly controllable and

ﬂexible for modiﬁcations [

]. The recon

ﬁgurable power system

is one of the proposed concepts to increase the controllability of the

existing power system [

,

17

]. It is expected that the SPVS based

recon

ﬁgurable systems will play a major role in future distribution

networks.

This review paper starts with presenting the recon

ﬁgurable approach

with the advantages and different modes of operation. Then the appli-

cations of recon

ﬁgurable approaches on solar PV systems such as

recon

ﬁgurable PV arrays, power conditioning unit (DC/DC converter,

DC/AC inverter), microgrid controller and topology of distribution

network are presented with related studies. An analysis is also presented

considering the unique features of recon

ﬁgurable systems in comparison

to the static systems.

The paper is organized as follows: Section

presents solar PV systems,

associated components, and different solar microgrid architecture high-

lighting their functions for which recon

ﬁgurable concept can be applied.

Based on that, section

presents a critical discussion on recon

ﬁgurable

solar PV systems. This discussion is supported by a summary on the

recon

ﬁgurable systems, their advantages and a cost analysis. Then sec-

tion

presents a conclusion of this study.

* Corresponding author.

E-mail address:

udayanga@uom.lk

(K.T.ManjulaU. Hemapala).

Contents lists available at

ScienceDirect

Heliyon

journal homepage:

www.cell.com/heliyon

https://doi.org/10.1016/j.heliyon.2020.e05530

Received 13 May 2020; Received in revised form 30 August 2020; Accepted 12 November 2020

2405-8440/

http://creativecommons.org/licenses/by-

nc-nd/4.0/

Heliyon 6 (2020) e05530

2. Solar photovoltaic systems

Solar PV generation has become more prominent in addressing rural

electri

ﬁcation requirements through standalone solar PV systems

(SPVSs). Later, considering the environmental bene

ﬁts and the

increasing trend of economic value with the technological development,

SPVSs were connected to the utility grid. Therefore, two main types of

SPVSs can be identi

ﬁed as standalone SPVSs and grid connected SPVSs.

In this study, grid connected SPVSs are under concern. Depending on the

functions and system architecture, grid connected SPVSs can be catego-

rized as rooftop SPVSs and solar farms. The system architectures of those

systems are shown in

Figure 1

Generally, a rooftop SPVS can be a home system or an industrial

system or a commercial building-mounted system, which intends to

supply the local demand and to transmit available excess power to the

main grid. Nevertheless, solar PV farms do not feed the local loads and

directly supply power to the utility grid. SPVSs are connected to the

utility grid through low or medium voltage distribution network or the

high voltage transmission network. According to the scale of the SPVS,

we can identify three scales as utility-scale (above 1MW), medium-scale

(1MW-10kW) and small scale (below 10kW) SPVSs. Generally, solar

farms are connected to the medium voltage distribution system or high

voltage transmission network. SPVs for industrial or commercial

buildings are medium-scale SPVs that are connected to the medium or

low voltage distribution network. SPV home systems are considered as

small-scale SPVs and they are connected to the low voltage distribution

network.

Figure 2

illustrates the connections of each speci

ﬁed SPV to the

utility grid.

2.1. Solar photovoltaic module

A solar PV cell shows a non-linear characteristic. Therefore, an

appropriate model is required to represent the electrical characteristics of

solar PV cells, rather than representing through a single current or a

Figure 1. Solar PV system architectures (a) Solar farm (b) Rooftop solar PV.

Figure 2. Structure of (a) conventional utility grid (b) with the connection of different types of solar.

Figure 3. Electrical equivalent 5 parameter model based on one diode theory.

Figure 4. I

–V characteristics.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

voltage source. The 5- parameter model is the most used model due to its

simplicity and accuracy. This model is shown in

Figure 3

[

I ¼ I

PV;Cell

s;Cell

ðexp

aVt

1Þ

(1)

The

ﬁrst term in

Eq. (1)

, is proportional to the irradiance intensity

whereas the second term, the diode current, expresses the non-linear

relationship between the PV cell current and voltage. According to the

equations, solar PV characteristics depend on different factors such as

solar irradiation and cell temperature as shown in

Figure 4

2.2. Power conditioning unit

The main function of the power conditioning unit (PCU) is converting

generated Solar DC power into usable AC power. The PCU typically

consists of a DC-DC converter and a DC-AC inverter. The DC and the AC

sides are connected to solar PV generator and the utility grid or AC load

respectively. Special circuit breakers, input

ﬁlters, etc. are also interfaced

in a PCU depending on the applying conditions and the ripple current.

PCU is an important subsystem in designing SPVSs, since the number

of inverters and power conversion stages and their con

ﬁgurations

signi

ﬁcantly affect the performance, reliability, mismatch rejection and

costs of the system. In practical scenario, different architectures are

available for the SPVSs depending on the type of the power conditioning

unit. The mostly used architectures are central inverter, string inverter,

multi-string inverter and modular inverter [

] as shown in

Figure 5

According to the IEEE standard 1547, the speci

ﬁed operational limits

of grid connected solar PV system are as in

Table 1

In literature, different types of solar inverters can be found. According

to them, mainly three kinds of solar inverters are available. Two of them

are traditional inverters namely Voltage Source Inverter (VSI) and Cur-

rent Source Inverter (CSI). The other one is a trending inverter that is

called as impedance Source Inverter (ZSI). ZSI was introduced to over-

come issues with aforementioned traditional inverters such as inverter

failures during shoot through stage, having single stage power conver-

sion with single controllable parameter (Modulation index only) [

ZSI is capable of both DC-DC and DC-AC conversions within the same

inverter having two controllable parameters; Modulation index and

shoot through duty. However, the harmonic injection to the network is

one of the issues related to solar inverters. Nowadays many researches

are interested in increasing the performance of PCU.

Maximum Power Point Tracking (MPPT)

To achieve MPP, different controlling methods are proposed in the

literature. There are well recognized MPPT methods in the literature that

are proposed to achieve MPP in solar PV systems under uniform irradi-

ance condition and Partial Shading Conditions (PSC) [

].

There is an important consideration of the maximization of energy

capture by solar panels. Therefore, solar tracker designing has come into

the picture. There are several studies on the performance evaluation of

solar trackers. Technical and economic performances of solar trackers for

different solar irradiation levels are analyzed under [

]. This study is

mainly focused on medium and high latitude countries in the northern

hemisphere. Another important study on solar trackers is ranking avail-

able trackers considering the energy output and the levelized cost of

electricity [

]. This provides a suitable platform for the designers on low

latitude countries in African, Asian and American continents. A similar

approach is presented in [

], in evaluating the solar tracker perfor-

mance with the latitude. Likewise, many useful studies have been done

for the bene

ﬁt of the designers in including solar trackers in their system

designing.

2.3. Problems associated with grid connected SPVS

Nowadays there is an emerging trend to integrate solar PV arrays to

the low voltage system with the governmental intervention. But there are

critical issues that are inherent to SPVS to be solved. These critical issues

can be discussed in the grid point of view and SPVS point of view by

considering each subsystem of SPVSs as presented by

Figure 6

. The main

aim of this section is to introduce possible impacts that SPVSs may

impose on the network.

2.3.1. Reverse power

ﬂow

With the introduction of distributed generation sources such as SPV to

the utility network, traditional centralized power generation architecture

Figure 5. SPV architectures (a) Central inverter (b) String inverter (c) Module inverter (d) Multi-string inverter.

Table 1. IEEE standard 1547: Operational limits.

Feature

Limitation

Maximum output voltage

6% of the nominal grid voltage

Frequency range

1% of the nominal frequency

Total harmonic distortion

THD

Power factor

0.9 lagging

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

transforms into a hybrid power generation architecture. Under a high

penetration scenario, daytime solar generation results in surplus power,

which is exported to a neighbouring feeder or the transmission lines. This

causes a reverse power

ﬂow in distribution substation levels, feeders, and

sections. Generally, the distribution feeders of the distribution network

are designed only for unidirectional power

ﬂow. As a result, the over-

current protection coordination and the operation of voltage regulators

may get affected. Suitable protection methods should be implemented for

feeders to overcome these issues by considering feeder basis studies and

allowing bidirectional power

ﬂow as proposed in the literature [

2.3.2. Power quality problems

The critical problems related to grid-connected systems are voltage

variations and harmonic problems.

Voltage problems

Voltage

ﬂuctuations are resulted by rapid variations of solar irradia-

tion and cloud passing. As the SPV penetration increases, the subjected

distribution network may get vulnerable to signi

ﬁcant voltage ﬂuctua-

tions. The reverse power

ﬂow due to excess solar power generation or

operating at a unity power factor without considering the reactive power

requirements may lead to a voltage rise in the distribution network [

]. The magnitude of the voltage rise is affected by the feeder

con

ﬁguration, the distance between the distribution feeder and the SPV

source along the feeder path, the connections of

ﬁxed capacitors and the

level of solar irradiation. In industrial practice, the absence of voltage

regulation functions results in solar generation spillage or unintentional

islanding situations which may cause interruptions to the penetration of

sustainable power generation into the main power system. According to

IEEE Std. 519-1992, limitations on the voltage at PCC and islanding

conditions are given in

Table 2

[

This problem has been minimized by implementing controllable,

switched capacitors instead of

ﬁxed capacitors and lowering the voltage

reference of existing load tap changers (LTCs) and line voltage regulators

(LVR) [

]. However, rapid voltage

ﬂuctuations may result in the

frequent operation of LTCs, LVRs and voltage-controlled capacitor banks.

This will reduce the life expectancy of each voltage regulator and require

frequent maintenance [

].

In addition to these solutions, allowing SPVS to control the reactive

power, distributed network recon

ﬁguration, clustering distribution

network into several microgrids including SPV and creating SPV based

microgrids are proposed in [

] and these solutions can be identi

ﬁed as the

most effective solutions in reducing the limitations on the integration of

distributed generation sources to the grid. In addition to that,

photovoltaic-electrical vehicle (PV-EV) novel technique is proposed in [

].

Harmonics

This problem is a critical power quality issue that appears due to the

involvement of a power electronic inverter based SPVS. A solar power

conversion unit is the heart of the SPVS that has been implemented with

power electronic-based components. Harmonics are generated as a result

of the switching operation of DC/AC power conversion. Signi

ﬁcant

harmonic injection to the utility grid may result in parallel and series

resonances, overheating of capacitor banks and transformers and false

operation of protection devices. In IEEE Std. 519-1992, the possible

maximum harmonic levels are speci

ﬁed. According to that, the total

harmonic distortion of the voltage (THDv) should be below 5% and in-

dividual THD should be below 3% [

According to many researches, well-designed harmonic

ﬁlters,

multilevel inverters, z-source inverters, and DC microgrids are the most

promising solutions. At present, the harmonic levels of most of the

modern PWM inverters are considerably low (below 3% THD). This

ﬁgure is better than that of the distribution networks, as most of the loads

connected to distribution networks consist of recti

ﬁer front ends [

].

According to [

], the maximum possible penetration of SPV (with THDi

<2%) into the distribution network was determined as 60% of rated

power from the power transformer by considering the limits of harmonic

distortion voltage of the distribution network.

2.3.3. Power availability

The contribution of SPV in addressing demand is limited to the day-

time. But the peak demand of most power systems occurs in the night

time. Therefore, this expensive asset cannot be utilized as a peak shaver.

However, different solutions have been introduced in increasing the

effective utilization of SPV. The following techniques are some of the

solutions which are introduced to the existing power system structure to

absorb the excess PV production.

Energy storage-different types of energy storage devices have been

proposed in literature such as battery energy storage, pump storage

power plants, etc.

Figure 6. Problems with grid-connected solar PV systems.

Table 2. IEEE STD.519-1992: Voltage limitations and requested time for

Islanding.

Voltage (at point of utility connection)

Maximum trip time

V

< 50%

0.1s

50%

< V < 85%

2.0s

85%

< V < 110%

Continuous operation

110%

< V < 135%

2.0 s

135%

> V

0.05 s

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

Load shifting - shifting suitable loads to meet the excess generation

with the modernization of the power system into the smart grid

concept by increasing the controllability of the power system.

2.3.4. System capacity

Solar power generation is limited in the daytime. But, in most of the

developing countries, due to the increase of domestic activities, the peak

demand occurs at night time. Even though there are grid-connected SPVS

which can be utilized as peak shavers, the capacity of the transmission

and distribution system of the country should be expanded to supply the

peak load. The maximum bene

ﬁts of an SPVS cannot be achieved without

energy storage devices or peak shifting methods at the load side.

2.3.4.1. Power losses.

The main problem regarding SPVS is that the

actual energy extracted from SPV is lesser than its potential energy

generation. This occurs as a result of the electrical mismatch of the SPV

array, the impedance mismatch between the solar PV system and the load

and power conversion losses in the complete system.

2.3.5. Impedance mismatch losses

The characteristics of an SPV module vary with the heat and insola-

tion. To extract the maximum power from an SPV module, impedance

mismatch losses should be minimized. Impedance mismatches reduce the

overall conversion ef

ﬁciency of an SPV array. Therefore, maximum

power point trackers (MPPTs) are used with solar arrays. These MPPTs

are dc/dc converters that utilize MPPT algorithms to track the MPP,

under dynamic environmental conditions.

SPV is considered as an intermittent power source as its power output

varies with the time of generation. Availability of solar power generation

only during the day time, inability to cater to the night peak, less

controllability, etc. are some of the common issues associated with SPVS.

Consisting of several power conversion stages, poor fault tolerance

capacity [

], limitations of energy storage capacity and optimum

operation are some of the critical issues that are associated with SPV

architecture. A higher voltage stress on the inverter and harmonics in-

jection to the power network are the other drawbacks in existing SPV

inverters [

,

35

]. Initially, SPV inverters are modules that inject

power into the utility grid. Later on, newer designs have been introduced

to emphasize safety, to support intelligent grid integration and to reduce

the cost. Designers are looking forward to exploring new technology,

which has not been used in existing solar inverter modules, to further

improve the performance and reduce the cost.

2.3.6. Power conversion losses

A conventional SPVS consists of a single power conversion stage

which is dedicated for DC/AC conversion. Although a voltage level is

speci

ﬁed for the operation, higher or lower voltages may present in the

system. Therefore, a line transformer or a high-frequency transformer or

a buck or a boost converter can be used to overcome this issue. These are

the additional power losses associated with the power conversion ar-

chitecture. As in literature, the Z source inverter based SPVS has achieved

satisfactory results to overcome this problem [

2.4. PV microgrid

In electrical power systems, different types of SPVSs are found such as

grid connected and off-grid SPVSs, solar farms, rooftop SPVS and PV

microgrids. The relationship of solar PV MG with other SPVSs is given in

Figure 7

A microgrid is a group of interconnected loads and distributed

energy resources within clearly de

ﬁned electrical boundaries that act as

a single controllable entity for the grid. It operates in both grid-

connected and island modes. A solar photovoltaic microgrid (PV MG)

is de

ﬁned as a group of interconnected loads and SPVSs which acts as a

single controllable entity and operates in both grid-connected and

islanded conditions. Generally, a conventional SPVS is unable to

operate in the islanded mode on its own. However, this problem can be

addressed with a battery energy storage such that, a solar PV MG

consists of SPVSs, battery storage units, controllable loads and con-

trollers. A comparison between solar home systems and solar PV

microgrids is given in

Table 3

2.5. PV microgrid architecture

PV microgrid architectures can be classi

ﬁed in different ways based

on various facts as follows.

Considering boundary of microgrid,

According to the customer base,

❖ Single customer microgrid architecture

o Type of customer

■

Residential (home) PV microgrid

■

Commercial building microgrid

■

Industrial microgrid

❖ Multiple customer microgrid architecture

o According to the geographical area,

■

Feeder microgrid architecture

■

Partial feeder microgrid architecture

Considering the microgrid itself,

Power Architecture (the power ﬂow);

❖ According to the type of the power lines,

o AC power architecture

o DC power architecture

o DC-AC power architecture

❖ According to the nature of sources,

o Solar-Battery based power architecture

o Solar -Wind-based power architecture

o Solar - diesel-based power generator architecture

o Solar

– mini - hydro based power architecture

Control Architecture (According to communication and control data

ﬂow),

o Centralized control architecture

o Decentralized control architecture

o Hierarchical Architecture

o Multi-agent-based MG control architecture

o Recon

ﬁgurable Control Architecture

Figure 7. Relationship of PV microgrid with other Solar PV.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

Solar microgrids are categorized as single and multiple customer

microgrids depending on the customer base of the microgrid. Single

customer microgrids are powered through rooftop solar PV systems while

multiple customer microgrid are powered through rooftop solar PV sys-

tems or solar farms or both of them. Generally, single customer based

microgrids may be home microgrids or commercial building microgrids

or industrial microgrids while multiple customer microgrids may be

partial feeder microgrids. Full feeder microgrids are based on the number

of customers and the geographical area.

Figure 8

shows possible elec-

trical boundaries and PV microgrids according to the customer base [

].

Based on the involvement of AC and DC systems, there are different

PV- microgrid architectures as AC PV-microgrid, DC PV-microgrid and

hybrid PV-microgrid and can be illustrated as in

Figure 9

. In AC PV-

microgrids, the main bus is an AC bus where AC loads are directly con-

nected while DC power sources (solar and battery) and DC loads are

connected through DC/AC inverters and AC/DC converters respectively.

In DC PV-microgrids, the main bus is a DC bus where DC loads are

directly connected while DC sources (solar and battery) and AC loads are

connected through DC/DC converters and DC/AC inverters respectively.

However, a hybrid PV-microgrid is a combination of both AC and DC PV-

microgrids with bidirectional converters [

].

Based on the control architecture, PV MG architecture can be re-

categorized as follows [

Centralized control architecture

Decentralized control architecture

Hierarchical control architecture

Multi-agent control architecture

Reconﬁgurable Control Architecture

In the centralized concept, the sources are controlled by a central

controller which may place at a remote location. In the decentralized

concept, each source is individually controlled to share the demand

change, without any interaction between controllers. The multilayer

(hierarchical) control architecture is a better approach to overcome most

of the issues associated with centralized and decentralized control. A

multi-agent-based system is an advanced version of a decentralized sys-

tem in which controllers interact with each other in achieving microgrid

functions. The recon

ﬁgurable control architecture is the latest concept

which increases the reliability,

ﬂexibility and controllability of power

systems to use available resources in an optimized way to get reliable

power supply while having cost bene

ﬁts.

3. Recon

ﬁgurable solar PV microgrids (RSPVMGS)

Recon

ﬁgurable systems have the ability to change their conﬁgura-

tions depending on the operational conditions. This concept is bene

ﬁcial

for the systems in which the con

ﬁgurations are easily convertible. The

introduction of recon

ﬁgurability enhances system reliability, capacity

together with further system developments [

Today, most of the power system components do not solely come up

with hardware such that these components are interconnected with

different controlling and monitoring systems. Existing traditional ap-

proaches are no longer suf

ﬁcient to meet the evolving controlling and

monitoring requirements of the modern systems. A modern power system

requires a dynamic wide-area view, fast and predictive analytics and system-

wide coordination. Therefore, moving towards recon

ﬁgurable power sys-

tem components is the solution to ful

ﬁl future requirements. Reconﬁgur-

ability can be introduced to a power system at the hardware level as well as

in the control level to adapt to the on-demand functional requirements

through changing its hardware topology or control methodology.

Different recon

ﬁgurable solutions are available for different sections

of SPVSs such as PV array, power conversion unit and PV connected

microgrids, and the summary of the discussion is in

Figure 10

and

Figure 11

Table 3. Features of solar PV microgrid over a solar home system.

Solar home systems

Solar PV microgrid

Loads highly depend on the grid supply and

intermittent, uncontrollable SPV

generation.

Power supply to the loads can be

maintained even when the SPV power is

not available.

Utility grid has to undergo more stresses in

supplying the night peak

Reduce the stress on the grid during the

night peak (peak shaving).

System capacity should bare the peak

demand.

Have the ability to control loads such that

the consumption from the utility grid can

be reduced.

Figure 8. Different PV microgrid structures.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

3.1. The recon

ﬁgurable operation for solar PV array

The solar PV array recon

ﬁguration is one of the solutions for electrical

mismatch losses in an SPVS such that recon

ﬁgurable systems change the

inter-connections between the solar modules in a solar PV array.

Recon

ﬁguration approach is applicable only for central inverters, string

inverters and multi-string inverters. Generally, module inverters do not

follow this approach since the electrical mismatch problem does not

create a signi

ﬁcant effect on these inverters. According to the conﬁgu-

ration of connections of solar PV modules in a solar PV array, they can be

categorized as,

Series

Parallel

Series-Parallel

Honeycomb

Total cross-tied

Bridge-linked

Figure 12

illustrates these con

ﬁgurations. Series and parallel con-

nections are the basic con

ﬁgurations that are used to provide the

required power output. Other con

ﬁgurations are modiﬁed versions of

basic con

ﬁgurations which are designed to minimize the partial shading

effect while providing the same power output as the basic con

ﬁgurations

[

19

,

In literature, ample research papers were published related to this

research area. Most of these researches are focused on series-parallel (SP)

and total-crossed-tied (TCT) con

ﬁgurations. As a reconﬁguration

approach, most of the researchers have used the irradiance equalization

technique as a control objective [

,

46

]. The recon

ﬁgurable array

basic structure is as in

Figure 13

[

3.2. The recon

ﬁgurable operation for power conditioning unit

In an SPVS, the solar inverter is the main controllable device that is

engaged in maximum power point tracking (MPPT) and grid synchro-

nization in addition to the DC/AC conversion. Different types of solar

inverters have been proposed considering different perspectives. Out of

these proposed inverter types, the recon

ﬁgurable solar inverter has

drawn signi

ﬁcant attention and this concept can be applied not only for

DC/AC inverters but also for DC/DC converters.

3.2.1. Recon

ﬁgurable solar converter

In [

48

], a new concept called Recon

ﬁgurable Solar Converter (RSC) is

under discussion. It is a conventional 3-ph SPV converter, with a mini-

mum modi

ﬁcation to the utility-scale. Its system conﬁguration is an SPV

plant type with a battery backup. The system structure of the proposed

converter is given in

Figure 14

. This system consists of an SPV array, a

battery backup, a conventional 3-ph inverter, a harmonic

ﬁlter, a trans-

former and additional switches. Here, the recon

ﬁgurable unit is a

single-stage power conversion unit and its controllability has been

improved to change its con

ﬁgurations according to the requirements of

the grid and the battery, and the availability of SPV generation. The

proposed power conversion unit has the ability to operate in

ﬁve major

modes of operations through additional switching. These modes are,

PV to the grid - SPV provides power supply to the grid.

PV to the battery - SPV provides power supply for the charging of the

battery.

PV-Battery to the grid - Both SPV and battery supply power to the

grid.

Battery to the grid - Battery is sending power to the grid.

Grid to the battery - Battery is charging from the grid supply.

Here, recon

ﬁguration is proposed to improve the power conversion

ﬁciency compared to the dual-stage power converter and to maximize

the utilization, whenever the peak shifting is required. Therefore, it is

expected that the proposed converter could reduce its cost, weight, and

volume, and also support the economic dispatch requirements. As dis-

cussed, the new converter adds technical,

ﬁnancial and economic values

to the conventional SPVS and can be applied to both SPV home systems

and MGs.

Figure 9. PV microgrid structures according to AC/DC systems (a) AC micro-

grid (b) DC microgrid (c) Hybrid microgrid.

Figure 10. Summary of the function of recon

ﬁgurable solar PV systems.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

A comparison between the performances of a microgrid connected

RSC and conventional two-stage inverter (TSI) with a bidirectional

converter for battery power controlling, is presented in [

]. According

to this comparison, the RSCs have more economic bene

ﬁts together with

an improved controllability over TSIs under the same power output

conditions.

Another application of RSC has been proposed in [

] for a distrib-

uted PV-battery architecture by considering a solar farm, to reduce the

effect of the intermittent nature of SPV generation. Here, RSC in [

] is

Figure 11. Summary of the application of recon

ﬁgurable solar PV systems.

Figure 12. Recon

ﬁgurable array basic structures (a) Series (b) Parallel (c)Se-

ries-Parallel (d)Total-cross-tied (e) Bridge-linked (f) Honeycomb.

Figure 13. Recon

ﬁgurable array basic structure.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

modi

ﬁed to a single-phase RSC such that it can be used for peak shifting.

The same modes of operation in [

] apply to this model. These modi

ﬁed

modular RSCs are connected in series with an additional battery backup

to eliminate the grid side transformer. Therefore, the proposed archi-

tecture does not contain a transformer and this may result in reduced

power losses and costs. Due to its modular nature, RSCs have the ability

to independently control each array and allow the connection of small

and multiple energy storage systems. There is a separate energy storage

system that is used in smoothing the power

ﬂow variations through a

ramp rate control.

Recently, a new inverter topology for solar-powered AC/DC hybrid

homes has been developed by improving the concept of RSC in [

].

The main consideration of this new inverter is to reduce the harmonic

distortion which is created due to the extra power conversion in

supplying DC load from DC power supply while achieving the

maximum utilization of utility-scale solar inverter. The performance

of each mode of operation and transitions between these modes are

under consideration. Total Harmonic Distortion (THD) can be

compared between these two scenarios; connecting a dc load to

additional DC-AC and AC-DC converters with the same rating and the

newly proposed topology. Developed topology has been practically

implemented and validated. A signi

ﬁcant harmonic reduction (by

16% from THD) and an ef

ﬁciency improvement have been achieved

by introducing a DC supply for DC loads (by creating a DC

microgrid).

3.2.2. Recon

ﬁgurable single-input dual-output converter

A new concept for recon

ﬁgurable single-phase converter is pro-

posed in [

]. It is introduced as a single-input dual-output (SIDO)

converter to supply DC loads that require high and low voltage levels

in domestic microgrid operation (electronic equipment, electric vehicle

charging, scooter charging). Here, a high DC voltage is required for

higher DC loads such as electric vehicle charging, scooter charging, and

a low DC voltage is required for smaller DC loads such as electronic

equipment. This newly proposed converter has the ability to operate in

three different modes by changing its con

ﬁguration through static

switches, depending on the availability of SPV generation and DC load

demand.

RES DC/DC SIDO mode - two different voltage supplies are provided

through solar power generation depending on the DC load demand

and solar power availability. As the name of this mode implies two

separate outputs are available as buck and boost converter outputs

with one input.

Grid/RES double DC output mode - Here, the SIDO converter has been

recon

ﬁgured into a separate H bridge converter and a buck converter.

Here, SPV is connected to smaller DC loads through a buck converter

and the grid supplies the large DC loads through an H-bridge

converter.

Grid double DC output mode - SIDO converter reconﬁgures into a

single input double cascade converter by a series connection of an H-

bridge converter and a buck converter. Static switches are available in

this model to feed two-levels of DC loads. Generally, the cost of an

Figure 14. Structure of recon

ﬁgurable solar converter.

Figure 15. Modes of operation of RSC (a) Structure of SIDO (b) Structure of

SIDO at RES DC/DC SIDO mode (c) Structure of SIDO at Grid/RES double DC

output mode (d) Structure of SIDO at Grid double DC output mode.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

equipment is directly related to the number of components of the

equipment. Therefore, this converter is implemented such that a low

number of associated components are required to achieve the grid

connected operation in the form of a microgrid. In addition to that,

maintaining the same system with the reduction of components in-

creases the utilization coef

ﬁcient of the system.

Structures for different modes of operation of RSC are given in

Figure 15

Figure 16. Structure of single-phase RSVPS.

Figure 17. qZSSRC (a) Structure of qZSSRC (b) Characteristics of qZSSRC.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

3.2.3. Recon

ﬁgurable PV system

In [

53

], another new concept for a single-phase RSPVS which is

equipped with a quasi Z-source inverter is proposed to maintain an un-

interrupted power supply to the loads in a case of grid failure. The pro-

posed system structure is given in

Figure 16

This recon

ﬁgurable system can be operated in two modes [

Grid-connected mode - normal operation of the grid-connected

inverter.

Standalone mode – when the grid is failed, the system gets discon-

nected from the grid and operates as a standalone system

Transients may appear in the system as the mode of operation

changes. Therefore, an indirect current controlling method has been

proposed to compensate these transients. The proposed indirect current

controlling method is implemented in the MATLAB/Simulink environ-

ment and tested under different loading conditions. The above proposed

recon

ﬁgurable model ensures system reliability in the case of grid failure.

3.2.4. Quasi-Z-source series resonant DC/DC converter

A recon

ﬁgurable operation method for a quasi-Z-source series reso-

nant DC/DC converter (qZSSRC) is proposed in [

]. The main consid-

eration is on MPP tracking of solar panels, under partial shading

conditions and different temperatures. Here, the incremental conduction

method can be used to calculate the reference input voltage. This con-

verter provides a wide range of input voltage and load regulation capa-

bility to the SPVS. The proposed system has the capability to change its

con

ﬁguration into two different conﬁgurations as a full-bridge converter

or a traditional series resonance converter (SRC) and a single switch

qZSSRC as given in

Figure 17

a and it is operated in following three

different modes depending on its point of operation.

Buck mode – The system shifts to this mode of operation, at the

startup of the qZSSRC and at low-temperature operating conditions.

Here, the system functions as a single switch quasi Z-source dc/dc

converter.

Normal mode - This is a boundary between buck and boost modes.

The system is operated as a full-bridge qZSSRC at the resonant fre-

quency in half cycle discontinuous conduction mode.

Boost mode - The system shifts to this mode of operation when the

system is operated at high-temperature and partially shaded condi-

tions. Here, the system functions as a full-bridge qZSSRC at the

resonance frequency in half cycle discontinuous conduction mode.

The characteristic curves of qZSSRC are shown in

Figure 17

As the main modi

ﬁcations, implementation of the magnetically in-

tegrated synchronous qZS-network and a resonant voltage-doubler

recti

ﬁer (VDR), a reconﬁgurable buck-boost switching stage and a spe-

cial control algorithm with smooth transitions between the operation

modes can be stated. The proposed control algorithm is intended to

achieve a desired dynamic behaviour in MPP tracking with smooth

transitions between three modes of operation. The peak ef

ﬁciency has

been improved by almost up to 97% at the nominal voltage (including all

losses in the converter). Here, the number of passive components and

switching devices which are in operation at a time are higher, when

compared to the other DC/DC converters. This can be highlighted as the

main disadvantage of this converter [

].

Figure 18. Structure of boost converter with recon

ﬁgurable inductor.

Figure 19. Structure of recon

ﬁgurable microgrid.

Figure 20. Proposed recon

ﬁgurable control architecture.

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

Table 4. Comparison of recon

ﬁgurable Solar PV systems/microgrid.

Micro grid

Advantages

Recon

ﬁgurable

section

Modes of operation

Added features

Validated through

RSC [

48

]

No, (Utility scale

solar PV power

plants)

Single power conversion

system to perform different

operation modes

The solar plants can be

controlled more effectively

and its power can be

dispatched more

economically due to

ﬂexibility of operation

Maximize its utilization and

reduced cost, volume and

weight

VSC (3ph)

1)PV to grid

2)PV to battery

3)PV-Battery to grid

4)Battery to grid

5)Grid to battery

Added additional

cables and mechanical

switches to

conventional the three-

phase PV inverter sys-

tem to operate as a dc/

dc converter in addi-

tion to its dc/ac

conversion.

Optional inductors are

included if the ac

ﬁlter

inductance is not

enough for the

charging purpose

The synchronous

reference frame

proportional-integral

current control is

employed for power

control

Hardware

implementation

RSC for

distributed PV-

Battery systems

[

]

No, (Utility

scale solar PV

power plants)

Possible for peak shifting

Possible for Smooth power

variation

Enable to connect different

types of PV modules and

small energy storage

systems

Reduced power conversion

losses by removing step up

transformer

VSC (1ph)

1)PV to grid

2)PV to battery

3)PV-Battery to grid

4)Battery to grid

5)Grid to battery

Grid side transformer is

removed from

distributed multilevel

modular RSC

Power controlled

through ramp rate

controlling method

Additional, separate

battery is used to help

ramp rate controlling

MATLAB -Simulink

simulation

RSC with DC

bus [

]

Yes (AC/DC,

domestic

microgrid)

Improves the efﬁciency,

reduces

volume, and enhances the

reliability.

Increased dc side of the

inverter ef

ﬁciency (90%)

than that of dc appliances

connected in ac side

(72

–80%)

Reduce 16% of current

harmonics

(THD)

VSC (1ph)

1)PV to grid

2)PV to battery

3)PV-Battery to grid

4)Battery to grid

5)Grid to battery

Same as RSC (Jha &

Triar, 2019), utilize

single conversion of ac

power to dc and vice

versa

DC loads are directly

connected to the DC

link without

connecting to AC side

through AC/DC

converter

Hardware

implementation

Recon

ﬁgurable

SIDO inverter

[

52

]

Yes (Domestic

Microgrid)

Flexible to operate different

power conversion modes

Solution to meet the

demand of mixed power

supply (AC and DC) with

single converter

desirable performance

under both steady-state and

transient conditions.

Reduced no of components,

maximize its utilization,

reduced cost, volume and

weight

Single-input

dual-output (SIDO)

converter (DC/DC

and AC/DC converter

(1ph))

1)RES DC/DC SIDO

mode

2)Grid/RES double

DC output mode

3)Grid double DC

output mode

Single input dual buck-

boost converter has

been modi

ﬁed adding

11 static switches

Measures have taken to

meet mixed power

supply demand (AC

and DC)

Supply two level of dc

loads demands

MATLAB -Simulink

simulation

Ref [

]

Yes

Enable to supply

uninterrupted power

supply for critical loads at

grid failure

Improved reliability of the

solar PV system

Quasi Z-source

inverter (DC/AC

converter (1ph))

1)Grid connected

mode

2)Islanded mod

Single-phase quasi-Z-

source inverter is used

as Solar PV converter

Indirect current

control-based

controller is developed

MATLAB -Simulink

simulation and

hardware

implementation

Recon

ﬁgurable

quasi-Z source

Inverter [

]

No

Capability of wide range

voltage regulation for MPP

tracking

Reduced power losses due

to partial shading and

impedance mismatch

Improved peak efﬁciency of

converter closed to 97%

Smooth transition between

three modes of operations

DC/DC converter

(quasi-Z source

Inverter)

1)Boost mode (full

bridge qZSSRC)

2)Normal mode (full

bridge qZSSRC)

3)Buck (single switch

qZSC)

Implementation of

magnetically

integrated

synchronous qZS

network and resonant

voltage-doubler recti-

ﬁer (VDR) and its spe-

ﬁc controller

Hardware

implementation

(continued on next page)

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

3.2.5. Z-source inverter

ZSI has become an interesting research area related to solar PV

inverter performance enhancement in terms of power quality, ef

ﬁciency

and reliability by minimizing the harmonics in the output, introducing

fewer power conversion stages and managing converter failures resulted

by inevitable shoot-through conditions and capacitor failures respec-

tively [

]. In addition to that, ZSI is used in grid connected and

islanded operation of SPVS together with reactive power controlling

[

59

]. As a novel approach, ZSI based MPPT is available for solar power

applications [

]. However, the combined operation of grid connected

mode and islanded mode while night time reactive power compensation

is not proposed for a residential system. Furthermore, solar PV systems

based recon

ﬁgurable systems will play a major role in future distribution

networks.

3.2.6. Recon

ﬁgurable inductor

Most of the researches are focused on the recon

ﬁgurability of the

entire converter. There is a low consideration of the recon

ﬁgurable

operation of a single element of a system. In [

], a recon

ﬁgurable

inductor is proposed as a solution for low-ef

ﬁciency solar PV boost

converters, under low insolation conditions with high current and

voltage ripples. This approach can also be used to overcome design

limitations on inductor sizing to prevent saturation at high insolation

levels. Here, the standard boost converter is modi

ﬁed with three switches

and replaced the inductor with a coupling inductor such that it can be

recon

ﬁgured into two different modes.

High-L - where, inductors are connected in series to reduce output

current and voltage ripple of the solar PV system at low insolation.

Low-L - where, inductors are connected in parallel. This mode of

operation prevents reaching saturation at high insolation levels.

Practically implemented models are available for SPVSs with

considerable power ef

ﬁciency improvements. It is useful to recharge

batteries of the standalone solar system to supply the loads under low

insolation levels. The structure of the converter is given in

Figure 18

Here, a two-stage power conversion architecture is under consideration.

3.3. Recon

ﬁgurable microgrids

The recon

ﬁgurability has been introduced for microgrid control ar-

chitecture as well as for microgrid topology architecture. Most of the

researches are based on battery-based inverters for microgrids such that

there is a low consideration towards AC generation including wind,

hydro and diesel generators. But recently, grid-connected SPV-battery

and hydro generation based recon

ﬁgurable systems have been proposed

[

61

]. The point of common coupling (PCC) is the common connection

point for the grid, the microgrid and the non

– linear loads in the system.

Table 5. Advantages of recon

ﬁgurable operation in power system.

For solar PV arrays

Technology [

,

44

]

For Solar PV systems

For microgrid

DC/DC converter [

,

60

]

DC/AC inverter [

,

51

]

Control architecture

[

]

Microgrid operation (Distribution

network) [

]

Solution for Electrical

mismatch

Solution for Electrical

mismatch [

Solution for Impedance

mismatch [

]

Solution for design Limitation

[

]

Maximize its utilization and

reduced cost,

volume and weight [

]

To improve power quality at PCC [

]

Maximize its utilization and reduced cost,

volume and weight [

,

51

]

To increase the reliability [

]

To increase

the reliability

Optimum MG operation

Distribution network power loss

reduction

Load balancing

Service restoration for critical loads

System ef

ﬁciency increased, power availability, power quality and power reliability at PCC is improved. Maximize its

utilization and reduced cost, volume and weight.

Reliability increased

Table 4 (continued )

Micro grid

Advantages

Recon

ﬁgurable

section

Modes of operation

Added features

Validated through

Ref [

60

]

No (residential

solar PV System)

Increasing solar energy

capture during low light

periods.

Smaller current ripple

without increasing the

volume to meet peak

current saturation

requirements.

Reduce the necessary PV

panel size, inductor

volume, or both.

Inductor in DC/DC

converter

1)High L (High

Inductance)

2)Low L (low

inductance)

A standard boost

converter has been

modi

ﬁed by replacing

source side inductor

from coupled two

inductors and adding 3

additional

semiconductor

switches.

Numerical

simulation and

hardware

implementation

Ref [

]

Yes (small hydro,

PV, battery

microgrid)

Extracting maximum power

from SPV system

Providing uninterrupted

power supply for critical

loads

Maintaining power quality

in the micro grid

The THD of load voltage

and grid current is below

5% even under nonlinear

loads

VSI (3ph)

1) Grid connected

mode

2) Islanded mode

Small hydro generator

was connected at PCC

Consideration the

effect of non-linear

loads

Compensation of load

reactive power.

The performance of the

recon

ﬁgurable system

has been veri

ﬁed under

all types of

disturbances

MATLAB -Simulink

simulation

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

Table 6. Cost saving methods of recon

ﬁgurable systems.

Reference

Application

Modes of

Operation

No. of

additional

switches

Circuit parameters

Cost saving from

[

]

Recon

ﬁgurable solar

converter (RSC) for

utility-scale PV-battery

application

Mode 1

—PV to

grid.

Mode 2

—PV to

battery

Mode 3

—PV/

battery to grid

Mode 4

—battery

to grid

Lithium

–ion Battery Parameters

Avoid separate DC/

converter for battery

charging

Battery Capacity

5.9 kWh/51.2Ahr

Battery nominal voltage

115.2 V

Min. Battery voltage

90 V

Max. Discharge current

52 A

Max. Pulse discharge current

150 A (

<2s)

Max. charging Voltage

132 V

Max. Charging current

10A

Inductance value of a coupled three-phase inductor in the dc/dc operation

DC Application

Inductance value

Only A

1.42 mH

Only B

1.58 mH

& C

0.50 mH

& B & C

0.13 mH

[

]

Recon

ﬁgurable Solar

Converter (RSC) for

Integration of energy

storage with a PV system

where ramp-rate control

and peak-shifting is

desired.

Mode 1

—PV to

grid.

Mode 2

—PV to

battery

Mode 3

—PV/

battery to grid

Mode 4

—battery

to grid

PV panel: (Sharp NU-U235F3) 235 Watt

DC-link capacitor for each cell: 3300

Inductance L ¼ 0.05 mH

Avoid separate DC/

converter for battery

charging

and it support for

ramp

rate controlling

[

]

A recon

ﬁgurable single-

phase inverter topology

for a hybrid

AC/DC solar powered

home.

Mode 1

—PV to

grid.

Mode 2

—PV/

battery to grid

Mode 3

—PV to

battery

Mode 4

—battery

to grid

Component

Avoid separate DC/

converter for battery

charging

and it allows DC

loads

Battery

12V, 9Ah

Filter Capacity (C1)

47uF

Filter Inductor (L1)

2.3mH

Switching frequency

4000 Hz

DC link Capacitor (C2) 2 nos

2200uF, 16 V

Resistance (R1)

Ω

Solar Panel

O/C Voltage (V)

22.09

S/C current (A)

8.36

Voltage at MPP (V)

17.7

Current at MPP (A)

7.62

Diode quality factor

1.25

No of series connected module per module

Number of modules per string

Series resistance (ohm)

0.165

Parallel resistance (ohm)

[

]

ﬂexible power

converter with static

switches that can change

the con

ﬁguration to

provide different

conversions with same

hardware structure.

RES DC/DC

SIDO mode

Grid/RES double

DC output mode

Grid double DC

output mode

Symbol

Description

Value

Enabling dual

renewable

source input

RSE Input

96V

Higher level output DC voltage

230V

Lower level output DC voltage

48V

Switching frequency

20kHz

inductance

5mH

Higher voltage level capacitance

1uF

Lower voltage level capacitance

1uF

[

]

A recon

ﬁgurable

photovoltaic system

based on the structure is

developed by combining

a single-phase quasi-Z-

source inverter and the

grid-connected system.

Grid Connected

Mode

Standalone

operation

Name

Speci

ﬁcation

Name

Parameter

Converter could

operate

either as a full-bridge

or a

single-switch quasi-

Z-source

dc-dc converter for

0.4%

California Energy

Commission

(CEC) weighted

energy

ﬁciency

improvement.

Rated output power

200W

Inductors L1, L2

3mH

Rated power of stand-alone

Load

100W

Capacitors C1, C2

470uF

Input Voltage

100V

Output Inductance L0

1.5mH

System Output Voltage

110Vrms/60hZ

Output Capacitance C0

4.75uF

Switching Frequency

12kHz

Power Switch

IRF840

(continued on next page)

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

Depending on the grid availability, the proposed recon

ﬁgurable micro-

grid is designed to be operated at two modes;

Grid-Connected mode

Islanded mode

Here, the recon

ﬁgurable operation is intended to be applied for the

control strategy of a microgrid. This recon

ﬁgurable system consists of

three different controllers as MPPT controller, bidirectional inverter

controller of battery energy storage system (BESS) and voltage source

converter (VSC) controller of the SPV system. But the solar inverter is

the main component that performs the recon

ﬁgurable operation by

changing the inverter control mode to the current controlling in the

grid-connected mode and to the voltage-frequency controlling in the

islanded mode. As a key feature of the above-proposed system, the

automatic synchronization of the microgrid to the utility grid while

providing an uninterrupted power supply for the critical loads, main-

taining the power quality in the microgrid and considering the effect of

non-linear loads can be highlighted. The recon

ﬁgurable microgrid

structure is given in

Figure 19

3.3.1. Recon

ﬁgurable control architecture

The next-generation PV inverters are intended to provide a variety of

new control features (e.g.; voltage regulation, power curtailment, ramp-

rate control, and communication-assisted protection) to enhance the

interaction between utility-scale PV-DG plants and the grid. This coor-

dinated controlling and operation can be achieved through localized or

utility-wide supervisory control systems.

In [

], a recon

ﬁgurable architecture is proposed for a microgrid

consists of distributed generation resources including SPV and power

backups. In this study, as control architectures, the conventional

centralized, decentralized and hierarchical architectures are under

consideration. The main aim of applying recon

ﬁgurable concept to the

control architecture is to ensure the microgrid operation even there are

failures in controllers, data transmission networks, etc. This control

architecture consists of four main control layers (local controller (LC),

emergency controller, secondary controller and global controller) and

an additional control layer called adversary control (ADVC) layer.

Here, the global and secondary layers reside in the master microgrid

controller (MMC) while the emergency control layer resides in ADVC,

MMC and LC. All controllers are interconnected via the communication

layer to operate as a centralized controller. According to the proposed

recon

ﬁgurable architecture, the microgrid is operated through a

decentralized controller. When a failure of LC occurs, the MMC func-

tions as a centralized controller. In an emergency, where both LC and

MMC are failed, ADVC functions as a centralized controller. The pro-

posed recon

ﬁgurable microgrid can be physically implemented and

tested for recon

ﬁgurable operation under various operating modes and

events. The corresponding recon

ﬁgurable control architecture is given

Figure 20

3.3.2. Recon

ﬁgurable distribution networks

With the introduction of distributed generation sources, the distri-

bution network has gained an active nature. High penetration of

distributed generation may lead to critical issues related to power reli-

ability, power quality, harmonic levels and protection. Voltage

Table 6 (continued )

Reference

Application

Modes of

Operation

No. of

additional

switches

Circuit parameters

Cost saving from

[

]

Novel soft-switching

galvanically isolated

buck-boost dc-dc

converter as a module

integrated converter for

photovoltaic

applications.

Normal mode

Boost mode

Buck mode

Input voltage range, V

…60V

Nominal input Voltage, V

34A

Maximal input current, I

12A

Input voltage range of boost mode

10...33V

Input voltage range of buck mode

…60V

Output voltage, V

400V

Switching frequency, f

105kHz

Resonant frequency, f

105kHz

Operating power range

25..250W

Component

Type

…S

, S

qzs

ﬁneon BSC035N10NS5

, D

CREE C3D02060E

Mi

11uH

qZS1

, C

qZS2

25uF

100uF

24uH

1mH

, C

66nF

12uF

Dead-time of inverter switches

200nS

Dead-time of S

qzs

70nS

[

]

A modi

ﬁed boost

converter with a

recon

ﬁgurable inductor is

presented for increasing

solar energy capture

during low light periods.

The self-inductance

¼ 215.9

¼ 215.8

series resistances around 100 m

The mutual inductance

12

¼ L

¼ 215.5

Reduced separated

inductor

for lower energy

production

to reduce harmonics

and increase energy

ﬁciency of the

inverter

K.A.Himali Lakshika et al.

Heliyon 6 (2020) e05530

ﬂuctuations, voltage ﬂickers, voltage sags, and dips and harmonics are

the main power quality issues related to SPVS.

In addressing these problems, recon

ﬁguration of the distribution

network into a cluster of microgrids or connecting distributed genera-

tions like solar and wind through microgrids can be identi

ﬁed as a

promising solution [

]. Moreover, it will lead to the reduction of the

power consumption from the utility grid.

The radial distribution network of the proposed system is subjected to

recon

ﬁgurability, focusing on energy costs and the frequency of supply

interruptions. This study highlights that to exploit the bene

ﬁts from the

recon

ﬁgurable approach, the most appropriate nodes for the microgrid

operations under certain conditions should be distinguished. This pro-

posed system is bene

ﬁcial to distribution system operators (DSOs) to up-

grade their services, exploit new businesses, and hold off investments on

modern networks. Microgrid regulators may also

ﬁnd this planning strat-

egy advantageous in terms of pro

ﬁts that can be gained through customer

operations and subsides for distribution system advancement [

3.3.3. Recon

ﬁgurable distribution networks into microgrids

The main aim of distribution network recon

ﬁguration is to advance

the microgrid operation with an economic load dispatch concept

considering the uncertainties of the system such as load variations and

the cost of SPV, wind generation and battery storage. And also vector

regression-based machine learning approaches can forecast such un-

certainties in the system. Vaccine-enhanced arti

ﬁcial immune system

(Vaccine-AIS) is a suitable multi-modal optimization technique to solve

the optimization problem related to this proposed model. The recon

ﬁg-

ured network has the capability to adjust its con

ﬁguration by itself. This

approach allows the maximum utilization of renewable energy while

reducing the power loss in the distribution network.

Recently, a new robust optimization technique has been introduced to

recon

ﬁgure distribution feeders into multiple microgrids for optimum

microgrid planning under system uncertainties [

]. It is proposed to

Download 3,22 Mb.

Do'stlaringiz bilan baham:

1 2 3